Conventionally, a X-ray inspection method for inspecting a connection state of a solder connection portion between a circuit device and a printed circuit board is disclosed in U.S. Pat. No. 6,823,040. A solder ball is formed in a lattice pattern on one side of the circuit device, and a land is formed on a position of the printed circuit board corresponding to the solder ball.
The X-ray inspection method disclosed in U.S. Pat. No. 6,823,040 includes a step of mounting a sample on a table, the sample in which the circuit device is mounted on the printed circuit board. Then, a X-ray source is arranged to face a X-ray detection portion with sandwiching the table therebetween. Then, the X-ray source and the X-ray detection portion are rotated while the X-ray source irradiates a X-ray toward the sample. Thus, a tomographic image along with a direction perpendicular to a principal surface of the printed circuit board is obtained. On the basis of the tomographic image, failure of the solder ball peeled off is detected.
In general, failure of the connection state of the solder connection portion between the solder ball and the land is a floating state in such a manner that the solder ball is completely separated from the land. Further, the failure includes a state that the solder ball is not completely melted so that the solder ball is partially bonded to the land. When the solder ball is partially bonded to the land, there is a possibility to break the solder connection portion with short time by temperature cycle load or vibration.
However, the shape of the solder connection portion in a state where the solder ball is partially bonded to the land has no critical difference from the shape of the solder connection portion between the solder ball and the land in a state where the solder ball is normally bonded to the land. In the inspection method disclosed in U.S. Pat. No. 6,823,040, the floating failure of the solder ball can be detected by using the tomographic image perpendicular to the principal surface of the printed circuit board. However, it is difficult to detect the failure that the solder ball is partially bonded to the land.
Further, the inspection method defines that the tomographic image in parallel to the principal surface of the printed circuit board can be obtained in addition to the tomographic image perpendicular to the principal surface of the printed circuit board. However, the inspection method does not define the failure that the solder ball is partially bonded to the land.